Submission #1138320

#	Time	Username	Problem	Language	Result	Execution time	Memory
1138320		anmattroi	Tracks in the Snow (BOI13_tracks)	C++17	12.08 / 100	1130 ms	614880 KiB

tracks

#include <bits/stdc++.h>
#define maxn 4005
#define fi first
#define se second
using namespace std;
using ii = pair<int, int>;

int n, m;
char a[maxn][maxn];
int cl[maxn][maxn];

int dv[4] = {0, 1, 0, -1};
int dh[4] = {1, 0, -1, 0};

int par[maxn*maxn];
int nho[maxn*maxn], id = 0;

int find_set(int v) {
    return par[v] < 0 ? v : par[v] = find_set(par[v]);
}

void union_set(int u, int v) {
    u = find_set(u); v = find_set(v);
    if (u == v) return;
    if (par[u] < par[v]) swap(u, v);
    par[v] += par[u];
    par[u] = v;
}

void bfs(int ox, int oy) {
    queue<ii> q;
    q.push(ii{ox, oy});
    cl[ox][oy] = ++id;
    while (!q.empty()) {
        auto [u, v] = q.front(); q.pop();
        for (int k = 0; k < 4; k++) {
            int i = u + dv[k], j = v + dh[k];
            if (1 <= i && 1 <= j && i <= n && j <= m && !cl[i][j] && a[i][j] == a[u][v]) {
                cl[i][j] = 1;
                q.push(ii{i, j});
            }
        }
    }

}

vector<int> adj[maxn*maxn];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    cin >> n >> m;
    for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++) cin >> a[i][j];

    fill(par+1, par+n*m+1, -1);

    for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
        if (a[i][j] != '.' && !cl[i][j]) bfs(i, j);

    for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++) for (int k = 0; k < 4; k++) {
        int u = i + dv[k], v = j + dh[k];
        if (1 <= u && u <= n && 1 <= v && v <= m && a[i][j] != '.' && a[u][v] != '.' && a[u][v] != a[i][j]) {
            if (find_set(cl[i][j]) == find_set(cl[u][v])) continue;
            adj[cl[i][j]].emplace_back(cl[u][v]);
            adj[cl[u][v]].emplace_back(cl[i][j]);
            union_set(cl[i][j], cl[u][v]);
        }
    }

    queue<int> q;
    nho[1] = 1;
    q.push(1);
    while (!q.empty()) {
        int u = q.front(); q.pop();
        for (int v : adj[u])
        if (!nho[v]) {
            nho[v] = nho[u]+1;
            q.push(v);
        }
    }
    cout << *max_element(nho + 1, nho + id + 1);



}

• Subtask 1: 3.3333 / 30
• Subtask 2: 8.75 / 70